As long as I see, Theatermode has TWO basic utilities.
First one: to use it as a Media Center, so the screen is used to display the cover, song info, and coming songs. For example: (Though everybody has its favourite display and configuration)

Second one: to use it as a 'Desktop' with a nice background and some basic info about the song (specially using the 'EndOfTrack' rotate setting) . I'm finding it really nice when chatting or skyping with friends. Though I think it could have much more uses (like distraction free writing, post-it board and similars)

Right now , to select one of them I have to go to the plugin folder and change the setting file and the backgrounds. Kind of quick, with a shortcut and copy-paste. But it would be great to be able to select one of them directly in MB...